This invention relates to a method and apparatus for obtaining measuring values which represent the thickness of a coherent fiber mass, particularly a sliver discharged by a carding machine or the like. The apparatus is of the type which utilizes an optical device comprising at least one light transmitter and at least one light detector between which the coherent fiber mass is passed.
In the field of textile fabric making, particularly in the spinning or spinning preparation processes it is frequently necessary to determine the thickness of slivers discharged by cards or drawing frames and to apply the measuring values to regulators. For determining the thickness of the fiber material, various principles are used such as capacitive, mechanical, pneumatic and sonic sensing. All known thickness determining apparatuses used so far have the disadvantage that their range of application is limited. Thus, according to a known apparatus, a light source (stroboscope) and a light detector (photocell/photodiode) are used for measuring the density of the material. In this apparatus the sliver passes through a tube in which diametrically opposite windows are provided. The high-intensity stroboscope irradiates with light pulses the fiber sliver which, being in overall contact with the tube, has a constant diameter. Dependent upon the density of the sliver, the intensity of the radiation varies. Thus, one part of the light rays is absorbed by the fibers and the light rays which are not absorbed by the fibers are measured by the detector. Such an apparatus is not adapted to measure the thickness of the sliver because, particularly in case of fiber slivers, the risks are high that an untrue thickness (diameter) is measured since it is based on the light which passes through the sliver. It is a further disadvantage that such a device is at least in part color-sensitive so that for fiber materials of a different color new reference and setting values have to be determined.